[dev.typeparams] all: merge master (8212707) into dev.typeparams

Conflicts:

- src/go/internal/gcimporter/iimport.go

  CL 325429 and CL 319931 made unrelated changes to adjacent lines

Merge List:

+ 2021-06-07 8212707871 crypto/elliptic: update P-521 docs to say it's constant-time
+ 2021-06-07 7406180012 fmt: split package documentation into more sections
+ 2021-06-07 e3176bbc3e crypto/tls: fix typo in Config.NextProtos docs
+ 2021-06-05 e1fa26026d spec: improve wording consistency by eliminating "specifier"
+ 2021-06-05 f490134126 spec: improve wording by choosing an official term "keyword"
+ 2021-06-05 e3cb381704 go/internal/gcimporter: don't waste CPU copying bytes in `io.ReadAll`
+ 2021-06-05 9d669ed47a misc/cgo/errors: use expected column numbers
+ 2021-06-04 95939e8de7 cmd/compile/internal/abi: fix typo in comment
+ 2021-06-04 831f9376d8 net/http: fix ResponseWriter.ReadFrom with short reads
+ 2021-06-04 3a9d906edc os: avoid finalizer race in windows process object
+ 2021-06-04 105c5b50e0 os: terminate windows processes via handle directly
+ 2021-06-04 79cd407f88 syscall: regenerate zsyscall_windows.go
+ 2021-06-04 c6b6211229 doc/go1.17: document testing changes for Go 1.17
+ 2021-06-04 0214440075 syscall: do not pass console handles to PROC_THREAD_ATTRIBUTE_HANDLE_LIST on Windows 7
+ 2021-06-04 962d5c997a cmd/compile,go/types: restrict use of unsafe.{Add,Slice} to go1.17 or newer
+ 2021-06-04 b29b123e07 cmd/compile: remove spurious ir.Dump
+ 2021-06-03 6d98301114 cmd/link: use correct alignment in PE DWARF sections
+ 2021-06-03 e0d029f758 runtime: avoid gp.lockedm race in exitsyscall0
+ 2021-06-02 dd7ba3ba2c net: don't rely on system hosts in TestCVE202133195
+ 2021-06-02 4f572d7076 io/fs: minor corrections to Sub docs
+ 2021-06-02 e11d14225c doc/go1.17: remove runtime section
+ 2021-06-02 6e189afd3e doc/go1.17: mention SYS_WAIT6/WEXITED on NetBSD
+ 2021-06-02 ff9f5fb859 cmd/link: recognize clang linker error in testCGOLTO
+ 2021-06-02 1c6a2ea2ea doc/go1.17: document time changes for Go1.17
+ 2021-06-02 d743e67e06 doc/go1.17: document flag changes for Go 1.17
+ 2021-06-02 dc8f87b749 runtime/internal/sys: generate //go:build lines in gengoos.go
+ 2021-06-02 84c0e5d47f cmd/link: move issue 43830 tests out of TestScript
+ 2021-06-02 cae68700cc runtime: fix formatting
+ 2021-06-01 567ee865f6 cmd/go: add declaration to cgo_lto_issue43830 test
+ 2021-06-01 24e9707cbf cmd/link, cmd/cgo: support -flto in CFLAGS

Change-Id: I9ef88e7de0f8b1841ed9604b613b41672df67e71

33 files changed, 525 insertions, 169 deletions

diff --git a/doc/go1.17.html b/doc/go1.17.html
index ee498f7603..7438d894fe 100644
--- a/doc/go1.17.html
+++ b/doc/go1.17.html
@@ -224,12 +224,6 @@ Do not send CLs removing the interior tags from such phrases.
   TODO: complete the Vet section
 </p>
 
-<h2 id="runtime">Runtime</h2>
-
-<p>
-  TODO: complete the Runtime section
-</p>
-
 <h2 id="compiler">Compiler</h2>
 
 <p><!-- golang.org/issue/40724 -->
@@ -434,7 +428,7 @@ Do not send CLs removing the interior tags from such phrases.
 <dl id="flag"><dt><a href="/pkg/flag/">flag</a></dt>
   <dd>
     <p><!-- CL 271788 -->
-      TODO: <a href="https://golang.org/cl/271788">https://golang.org/cl/271788</a>: panic if flag name begins with - or contains =
+      Flag declarations now panic if an invalid name is specified.
     </p>
   </dd>
 </dl><!-- flag -->
@@ -651,15 +645,22 @@ Do not send CLs removing the interior tags from such phrases.
       DragonFly and all OpenBSD systems (it was already defined on
       some OpenBSD systems and all FreeBSD, NetBSD, and Linux systems).
     </p>
+
+    <p><!-- CL 315281 -->
+      The constants <code>SYS_WAIT6</code> and <code>WEXITED</code>
+      are now defined on NetBSD systems (<code>SYS_WAIT6</code> was
+      already defined on DragonFly and FreeBSD systems;
+      <code>WEXITED</code> was already defined on Darwin, DragonFly,
+      FreeBSD, Linux, and Solaris systems).
+    </p>
   </dd>
 </dl><!-- syscall -->
 
 <dl id="testing"><dt><a href="/pkg/testing/">testing</a></dt>
   <dd>
     <p><!-- CL 310033 -->
-      TODO: <a href="https://golang.org/cl/310033">https://golang.org/cl/310033</a>: add -shuffle=off|on|N to alter the execution order of tests and benchmarks
+      Added a new <a href="/cmd/go/#hdr-Testing_flags">testing flag</a> <code>-shuffle</code> which controls the execution order of tests and benchmarks.
     </p>
-
     <p><!-- CL 260577 -->
       The new
       <a href="/pkg/testing/#T.Setenv"><code>T.Setenv</code></a>
@@ -689,15 +690,26 @@ Do not send CLs removing the interior tags from such phrases.
     </p>
 
     <p><!-- CL 264077 -->
-      TODO: <a href="https://golang.org/cl/264077">https://golang.org/cl/264077</a>: add Time.IsDST() to check if its Location is in Daylight Savings Time
+      The new <a href="/pkg/time/#Time.IsDST"><code>Time.IsDST</code></a> method can be used to check whether the time
+      is in Daylight Savings Time in its configured location.
     </p>
 
     <p><!-- CL 293349 -->
-      TODO: <a href="https://golang.org/cl/293349">https://golang.org/cl/293349</a>: add Time.Unix{Milli,Micro} and to-Time helpers UnixMicro, UnixMilli
+      The new <a href="/pkg/time/#Time.UnixMilli"><code>Time.UnixMilli</code></a> and
+      <a href="/pkg/time/#Time.UnixMicro"><code>Time.UnixMicro</code></a> methods return the number of milliseconds and
+      microseconds elapsed since January 1, 1970 UTC respectively.<br>
+      The new <code>UnixMilli</code> and <code>UnixMicro</code> functions return local Time corresponding to given
+      Unix time.
     </p>
 
     <p><!-- CL 300996 -->
-      TODO: <a href="https://golang.org/cl/300996">https://golang.org/cl/300996</a>: support &#34;,&#34; as separator for fractional seconds
+      The package now accepts comma "," as a separator for fractional seconds when parsing and formatting time.
+      The following time formats are now accepted:
+      <ul>
+        <li>2006-01-02 14:06:03,999999999 -0700 MST</li>
+        <li>Mon Jan _2 14:06:03,120007 2006</li>
+        <li>Mon Jan 2 14:06:03,120007 2006</li>
+      </ul>
     </p>
 
     <p><!-- CL 320252 -->
diff --git a/doc/go_spec.html b/doc/go_spec.html
index e59b3554f2..561d44271a 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -1,6 +1,6 @@
 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Version of Apr 28, 2021",
+	"Subtitle": "Version of Jun 2, 2021",
 	"Path": "/ref/spec"
 }-->
 
@@ -4909,7 +4909,7 @@ if x := f(); x &lt; y {
 
 <p>
 "Switch" statements provide multi-way execution.
-An expression or type specifier is compared to the "cases"
+An expression or type is compared to the "cases"
 inside the "switch" to determine which branch
 to execute.
 </p>
@@ -5020,7 +5020,7 @@ floating point, or string constants in case expressions.
 A type switch compares types rather than values. It is otherwise similar
 to an expression switch. It is marked by a special switch expression that
 has the form of a <a href="#Type_assertions">type assertion</a>
-using the reserved word <code>type</code> rather than an actual type:
+using the keyword <code>type</code> rather than an actual type:
 </p>
 
 <pre>
diff --git a/misc/cgo/errors/errors_test.go b/misc/cgo/errors/errors_test.go
index a077b59478..68a30a44fe 100644
--- a/misc/cgo/errors/errors_test.go
+++ b/misc/cgo/errors/errors_test.go
@@ -40,7 +40,8 @@ func check(t *testing.T, file string) {
 			if len(frags) == 1 {
 				continue
 			}
-			re, err := regexp.Compile(string(frags[1]))
+			frag := fmt.Sprintf(":%d:.*%s", i+1, frags[1])
+			re, err := regexp.Compile(frag)
 			if err != nil {
 				t.Errorf("Invalid regexp after `ERROR HERE: `: %#q", frags[1])
 				continue
diff --git a/misc/cgo/errors/testdata/err2.go b/misc/cgo/errors/testdata/err2.go
index 1d22401aee..a90598fe35 100644
--- a/misc/cgo/errors/testdata/err2.go
+++ b/misc/cgo/errors/testdata/err2.go
@@ -40,15 +40,15 @@ func main() {
 	C.foop = x // ERROR HERE
 
 	// issue 13129: used to output error about C.unsignedshort with CC=clang
-	var x C.ushort
-	x = int(0) // ERROR HERE: C\.ushort
+	var x1 C.ushort
+	x1 = int(0) // ERROR HERE: C\.ushort
 
 	// issue 13423
 	_ = C.fopen() // ERROR HERE
 
 	// issue 13467
-	var x rune = '✈'
-	var _ rune = C.transform(x) // ERROR HERE: C\.int
+	var x2 rune = '✈'
+	var _ rune = C.transform(x2) // ERROR HERE: C\.int
 
 	// issue 13635: used to output error about C.unsignedchar.
 	// This test tests all such types.
@@ -91,10 +91,10 @@ func main() {
 
 	// issue 26745
 	_ = func(i int) int {
-		return C.i + 1 // ERROR HERE: :13
+		return C.i + 1 // ERROR HERE: 14
 	}
 	_ = func(i int) {
-		C.fi(i) // ERROR HERE: :6
+		C.fi(i) // ERROR HERE: 7
 	}
 
 	C.fi = C.fi // ERROR HERE
diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index ae61725bc7..a73e998877 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -1638,6 +1638,8 @@ func (p *Package) gccCmd() []string {
 		c = append(c, "-maix64")
 		c = append(c, "-mcmodel=large")
 	}
+	// disable LTO so we get an object whose symbols we can read
+	c = append(c, "-fno-lto")
 	c = append(c, "-") //read input from standard input
 	return c
 }
diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 8c31d5b794..94152f4278 100644
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -168,8 +168,18 @@ func (p *Package) writeDefs() {
 			if *gccgo {
 				fmt.Fprintf(fc, "extern byte *%s;\n", n.C)
 			} else {
-				fmt.Fprintf(fm, "extern char %s[];\n", n.C)
-				fmt.Fprintf(fm, "void *_cgohack_%s = %s;\n\n", n.C, n.C)
+				// Force a reference to all symbols so that
+				// the external linker will add DT_NEEDED
+				// entries as needed on ELF systems.
+				// Treat function variables differently
+				// to avoid type confict errors from LTO
+				// (Link Time Optimization).
+				if n.Kind == "fpvar" {
+					fmt.Fprintf(fm, "extern void %s();\n", n.C)
+				} else {
+					fmt.Fprintf(fm, "extern char %s[];\n", n.C)
+					fmt.Fprintf(fm, "void *_cgohack_%s = %s;\n\n", n.C, n.C)
+				}
 				fmt.Fprintf(fgo2, "//go:linkname __cgo_%s %s\n", n.C, n.C)
 				fmt.Fprintf(fgo2, "//go:cgo_import_static %s\n", n.C)
 				fmt.Fprintf(fgo2, "var __cgo_%s byte\n", n.C)
@@ -1042,7 +1052,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		// This unpacks the argument struct above and calls the Go function.
 		fmt.Fprintf(fgo2, "func _cgoexp%s_%s(a *%s) {\n", cPrefix, exp.ExpName, gotype)
 
-		fmt.Fprintf(fm, "int _cgoexp%s_%s;\n", cPrefix, exp.ExpName)
+		fmt.Fprintf(fm, "void _cgoexp%s_%s(void* p){}\n", cPrefix, exp.ExpName)
 
 		if gccResult != "void" {
 			// Write results back to frame.
diff --git a/src/cmd/compile/internal/abi/abiutils.go b/src/cmd/compile/internal/abi/abiutils.go
index cb8e9d7b0f..b8ea1955d1 100644
--- a/src/cmd/compile/internal/abi/abiutils.go
+++ b/src/cmd/compile/internal/abi/abiutils.go
@@ -449,7 +449,7 @@ func (config *ABIConfig) ABIAnalyze(t *types.Type, setNname bool) *ABIParamResul
 // parameterUpdateMu protects the Offset field of function/method parameters (a subset of structure Fields)
 var parameterUpdateMu sync.Mutex
 
-// FieldOffsetOf returns a concurency-safe version of f.Offset
+// FieldOffsetOf returns a concurrency-safe version of f.Offset
 func FieldOffsetOf(f *types.Field) int64 {
 	parameterUpdateMu.Lock()
 	defer parameterUpdateMu.Unlock()
diff --git a/src/cmd/compile/internal/noder/noder.go b/src/cmd/compile/internal/noder/noder.go
index 2fb852b184..08c05a69be 100644
--- a/src/cmd/compile/internal/noder/noder.go
+++ b/src/cmd/compile/internal/noder/noder.go
@@ -886,9 +886,6 @@ func (p *noder) typeExpr(typ syntax.Expr) ir.Ntype {
 	if n == nil {
 		return nil
 	}
-	if _, ok := n.(ir.Ntype); !ok {
-		ir.Dump("NOT NTYPE", n)
-	}
 	return n.(ir.Ntype)
 }
 
diff --git a/src/cmd/compile/internal/typecheck/func.go b/src/cmd/compile/internal/typecheck/func.go
index f9ee686f9e..15756a47e4 100644
--- a/src/cmd/compile/internal/typecheck/func.go
+++ b/src/cmd/compile/internal/typecheck/func.go
@@ -999,6 +999,12 @@ func tcRecover(n *ir.CallExpr) ir.Node {
 
 // tcUnsafeAdd typechecks an OUNSAFEADD node.
 func tcUnsafeAdd(n *ir.BinaryExpr) *ir.BinaryExpr {
+	if !types.AllowsGoVersion(curpkg(), 1, 17) {
+		base.ErrorfVers("go1.17", "unsafe.Add")
+		n.SetType(nil)
+		return n
+	}
+
 	n.X = AssignConv(Expr(n.X), types.Types[types.TUNSAFEPTR], "argument to unsafe.Add")
 	n.Y = DefaultLit(Expr(n.Y), types.Types[types.TINT])
 	if n.X.Type() == nil || n.Y.Type() == nil {
@@ -1015,6 +1021,12 @@ func tcUnsafeAdd(n *ir.BinaryExpr) *ir.BinaryExpr {
 
 // tcUnsafeSlice typechecks an OUNSAFESLICE node.
 func tcUnsafeSlice(n *ir.BinaryExpr) *ir.BinaryExpr {
+	if !types.AllowsGoVersion(curpkg(), 1, 17) {
+		base.ErrorfVers("go1.17", "unsafe.Slice")
+		n.SetType(nil)
+		return n
+	}
+
 	n.X = Expr(n.X)
 	n.Y = Expr(n.Y)
 	if n.X.Type() == nil || n.Y.Type() == nil {
diff --git a/src/cmd/compile/internal/types2/builtins.go b/src/cmd/compile/internal/types2/builtins.go
index 8e13b0ff18..8f2d849ef5 100644
--- a/src/cmd/compile/internal/types2/builtins.go
+++ b/src/cmd/compile/internal/types2/builtins.go
@@ -579,6 +579,11 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 
 	case _Add:
 		// unsafe.Add(ptr unsafe.Pointer, len IntegerType) unsafe.Pointer
+		if !check.allowVersion(check.pkg, 1, 17) {
+			check.error(call.Fun, "unsafe.Add requires go1.17 or later")
+			return
+		}
+
 		check.assignment(x, Typ[UnsafePointer], "argument to unsafe.Add")
 		if x.mode == invalid {
 			return
@@ -675,6 +680,11 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 
 	case _Slice:
 		// unsafe.Slice(ptr *T, len IntegerType) []T
+		if !check.allowVersion(check.pkg, 1, 17) {
+			check.error(call.Fun, "unsafe.Slice requires go1.17 or later")
+			return
+		}
+
 		typ := asPointer(x.typ)
 		if typ == nil {
 			check.errorf(x, invalidArg+"%s is not a pointer", x)
diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go
index 50bf80ba59..bc49c6d804 100644
--- a/src/cmd/dist/test.go
+++ b/src/cmd/dist/test.go
@@ -722,14 +722,29 @@ func (t *tester) registerTests() {
 				},
 			})
 			if t.hasCxx() {
-				t.tests = append(t.tests, distTest{
-					name:    "swig_callback",
-					heading: "../misc/swig/callback",
-					fn: func(dt *distTest) error {
-						t.addCmd(dt, "misc/swig/callback", t.goTest())
-						return nil
+				t.tests = append(t.tests,
+					distTest{
+						name:    "swig_callback",
+						heading: "../misc/swig/callback",
+						fn: func(dt *distTest) error {
+							t.addCmd(dt, "misc/swig/callback", t.goTest())
+							return nil
+						},
+					},
+					distTest{
+						name:    "swig_callback_lto",
+						heading: "../misc/swig/callback",
+						fn: func(dt *distTest) error {
+							cmd := t.addCmd(dt, "misc/swig/callback", t.goTest())
+							cmd.Env = append(os.Environ(),
+								"CGO_CFLAGS=-flto",
+								"CGO_CXXFLAGS=-flto",
+								"CGO_LDFLAGS=-flto",
+							)
+							return nil
+						},
 					},
-				})
+				)
 			}
 		}
 	}
diff --git a/src/cmd/link/cgo_test.go b/src/cmd/link/cgo_test.go
new file mode 100644
index 0000000000..26ab802454
--- /dev/null
+++ b/src/cmd/link/cgo_test.go
@@ -0,0 +1,141 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"internal/testenv"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+// Issues 43830, 46295
+func TestCGOLTO(t *testing.T) {
+	testenv.MustHaveCGO(t)
+	testenv.MustHaveGoBuild(t)
+
+	t.Parallel()
+
+	for _, cc := range []string{"gcc", "clang"} {
+		for test := 0; test < 2; test++ {
+			t.Run(fmt.Sprintf("%s-%d", cc, test), func(t *testing.T) {
+				testCGOLTO(t, cc, test)
+			})
+		}
+	}
+}
+
+const test1_main = `
+package main
+
+/*
+extern int myadd(int, int);
+int c_add(int a, int b) {
+	return myadd(a, b);
+}
+*/
+import "C"
+
+func main() {
+	println(C.c_add(1, 2))
+}
+`
+
+const test1_add = `
+package main
+
+import "C"
+
+/* test */
+
+//export myadd
+func myadd(a C.int, b C.int) C.int {
+	return a + b
+}
+`
+
+const test2_main = `
+package main
+
+import "fmt"
+
+/*
+#include <stdio.h>
+
+void hello(void) {
+  printf("hello\n");
+}
+*/
+import "C"
+
+func main() {
+	hello := C.hello
+	fmt.Printf("%v\n", hello)
+}
+`
+
+func testCGOLTO(t *testing.T, cc string, test int) {
+	t.Parallel()
+
+	if _, err := exec.LookPath(cc); err != nil {
+		t.Skipf("no %s compiler", cc)
+	}
+
+	dir := t.TempDir()
+
+	writeTempFile := func(name, contents string) {
+		if err := os.WriteFile(filepath.Join(dir, name), []byte(contents), 0644); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	writeTempFile("go.mod", "module cgolto\n")
+
+	switch test {
+	case 0:
+		writeTempFile("main.go", test1_main)
+		writeTempFile("add.go", test1_add)
+	case 1:
+		writeTempFile("main.go", test2_main)
+	default:
+		t.Fatalf("bad case %d", test)
+	}
+
+	cmd := exec.Command(testenv.GoToolPath(t), "build")
+	cmd.Dir = dir
+	cmd.Env = append(os.Environ(),
+		"CC="+cc,
+		"CGO_CFLAGS=-flto",
+	)
+
+	t.Log("go build")
+	out, err := cmd.CombinedOutput()
+	t.Logf("%s", out)
+
+	if err != nil {
+		t.Logf("go build failed: %v", err)
+
+		// Error messages we've seen indicating that LTO is not supported.
+		// These errors come from GCC or clang, not Go.
+		var noLTO = []string{
+			`unrecognized command line option "-flto"`,
+			"unable to pass LLVM bit-code files to linker",
+			"file not recognized: File format not recognized",
+			"LTO support has not been enabled",
+			"linker command failed with exit code",
+			"gcc: can't load library",
+		}
+		for _, msg := range noLTO {
+			if bytes.Contains(out, []byte(msg)) {
+				t.Skipf("C compiler %v does not support LTO", cc)
+			}
+		}
+
+		t.Error("failed")
+	}
+}
diff --git a/src/cmd/link/internal/ld/ar.go b/src/cmd/link/internal/ld/ar.go
index 22f53a4df2..23915f9032 100644
--- a/src/cmd/link/internal/ld/ar.go
+++ b/src/cmd/link/internal/ld/ar.go
@@ -124,6 +124,10 @@ func hostArchive(ctxt *Link, name string) {
 
 			libgcc := sym.Library{Pkg: "libgcc"}
 			h := ldobj(ctxt, f, &libgcc, l, pname, name)
+			if h.ld == nil {
+				Errorf(nil, "%s unrecognized object file at offset %d", name, off)
+				continue
+			}
 			f.MustSeek(h.off, 0)
 			h.ld(ctxt, f, h.pkg, h.length, h.pn)
 		}
diff --git a/src/cmd/link/internal/ld/config.go b/src/cmd/link/internal/ld/config.go
index ae0d7520eb..20f1d0b8c1 100644
--- a/src/cmd/link/internal/ld/config.go
+++ b/src/cmd/link/internal/ld/config.go
@@ -241,6 +241,10 @@ func mustLinkExternal(ctxt *Link) (res bool, reason string) {
 		return true, "dynamically linking with a shared library"
 	}
 
+	if unknownObjFormat {
+		return true, "some input objects have an unrecognized file format"
+	}
+
 	return false, ""
 }
 
@@ -248,7 +252,7 @@ func mustLinkExternal(ctxt *Link) (res bool, reason string) {
 //
 // It is called after flags are processed and inputs are processed,
 // so the ctxt.LinkMode variable has an initial value from the -linkmode
-// flag and the iscgo externalobj variables are set.
+// flag and the iscgo, externalobj, and unknownObjFormat variables are set.
 func determineLinkMode(ctxt *Link) {
 	extNeeded, extReason := mustLinkExternal(ctxt)
 	via := ""
diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index e8f001ba8e..644faeb2fb 100644
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -343,10 +343,16 @@ var (
 const pkgdef = "__.PKGDEF"
 
 var (
-	// Set if we see an object compiled by the host compiler that is not
-	// from a package that is known to support internal linking mode.
+	// externalobj is set to true if we see an object compiled by
+	// the host compiler that is not from a package that is known
+	// to support internal linking mode.
 	externalobj = false
-	theline     string
+
+	// unknownObjFormat is set to true if we see an object whose
+	// format we don't recognize.
+	unknownObjFormat = false
+
+	theline string
 )
 
 func Lflag(ctxt *Link, arg string) {
@@ -1065,6 +1071,10 @@ func hostobjs(ctxt *Link) {
 		}
 
 		f.MustSeek(h.off, 0)
+		if h.ld == nil {
+			Errorf(nil, "%s: unrecognized object file format", h.pn)
+			continue
+		}
 		h.ld(ctxt, f, h.pkg, h.length, h.pn)
 		f.Close()
 	}
@@ -1855,6 +1865,14 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
 		return ldhostobj(ldxcoff, ctxt.HeadType, f, pkg, length, pn, file)
 	}
 
+	if c1 != 'g' || c2 != 'o' || c3 != ' ' || c4 != 'o' {
+		// An unrecognized object is just passed to the external linker.
+		// If we try to read symbols from this object, we will
+		// report an error at that time.
+		unknownObjFormat = true
+		return ldhostobj(nil, ctxt.HeadType, f, pkg, length, pn, file)
+	}
+
 	/* check the header */
 	line, err := f.ReadString('\n')
 	if err != nil {
@@ -1874,7 +1892,7 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
 			return nil
 		}
 
-		Errorf(nil, "%s: not an object file: @%d %02x%02x%02x%02x", pn, start, c1, c2, c3, c4)
+		Errorf(nil, "%s: not an object file: @%d %q", pn, start, line)
 		return nil
 	}
 
diff --git a/src/cmd/link/internal/ld/pe.go b/src/cmd/link/internal/ld/pe.go
index 3540c07da1..8eb4231c3a 100644
--- a/src/cmd/link/internal/ld/pe.go
+++ b/src/cmd/link/internal/ld/pe.go
@@ -475,7 +475,7 @@ func (f *peFile) addDWARFSection(name string, size int) *peSection {
 	off := f.stringTable.add(name)
 	h := f.addSection(name, size, size)
 	h.shortName = fmt.Sprintf("/%d", off)
-	h.characteristics = IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_DISCARDABLE | IMAGE_SCN_CNT_INITIALIZED_DATA
+	h.characteristics = IMAGE_SCN_ALIGN_1BYTES | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_DISCARDABLE | IMAGE_SCN_CNT_INITIALIZED_DATA
 	return h
 }
 
diff --git a/src/crypto/elliptic/elliptic.go b/src/crypto/elliptic/elliptic.go
index b8e5a3097d..f072960bfe 100644
--- a/src/crypto/elliptic/elliptic.go
+++ b/src/crypto/elliptic/elliptic.go
@@ -455,7 +455,7 @@ func initP384() {
 // Multiple invocations of this function will return the same value, so it can
 // be used for equality checks and switch statements.
 //
-// The cryptographic operations are implemented using constant-time algorithms.
+// ScalarMult and ScalarBaseMult are implemented using constant-time algorithms.
 func P256() Curve {
 	initonce.Do(initAll)
 	return p256
@@ -479,7 +479,7 @@ func P384() Curve {
 // Multiple invocations of this function will return the same value, so it can
 // be used for equality checks and switch statements.
 //
-// The cryptographic operations do not use constant-time algorithms.
+// The cryptographic operations are implemented using constant-time algorithms.
 func P521() Curve {
 	initonce.Do(initAll)
 	return p521
diff --git a/src/crypto/tls/common.go b/src/crypto/tls/common.go
index 77957ef82b..d561e61707 100644
--- a/src/crypto/tls/common.go
+++ b/src/crypto/tls/common.go
@@ -619,7 +619,7 @@ type Config struct {
 	// protocol will be one from this list, and the connection will fail
 	// if there is no mutually supported protocol. If NextProtos is empty
 	// or the peer doesn't support ALPN, the connection will succeed and
-	// ConnectionState.NegotiatedProtocol will be empty."
+	// ConnectionState.NegotiatedProtocol will be empty.
 	NextProtos []string
 
 	// ServerName is used to verify the hostname on the returned
diff --git a/src/fmt/doc.go b/src/fmt/doc.go
index d05ee519c3..c584cc9465 100644
--- a/src/fmt/doc.go
+++ b/src/fmt/doc.go
@@ -189,7 +189,7 @@
 	When printing a struct, fmt cannot and therefore does not invoke
 	formatting methods such as Error or String on unexported fields.
 
-	Explicit argument indexes:
+	Explicit argument indexes
 
 	In Printf, Sprintf, and Fprintf, the default behavior is for each
 	formatting verb to format successive arguments passed in the call.
@@ -211,7 +211,7 @@
 		fmt.Sprintf("%d %d %#[1]x %#x", 16, 17)
 	will yield "16 17 0x10 0x11".
 
-	Format errors:
+	Format errors
 
 	If an invalid argument is given for a verb, such as providing
 	a string to %d, the generated string will contain a
diff --git a/src/go/internal/gcimporter/gcimporter.go b/src/go/internal/gcimporter/gcimporter.go
index b74daca246..73cf6334fd 100644
--- a/src/go/internal/gcimporter/gcimporter.go
+++ b/src/go/internal/gcimporter/gcimporter.go
@@ -145,17 +145,14 @@ func Import(fset *token.FileSet, packages map[string]*types.Package, path, srcDi
 		err = fmt.Errorf("import %q: old textual export format no longer supported (recompile library)", path)
 
 	case "$$B\n":
-		var data []byte
-		data, err = io.ReadAll(buf)
-		if err != nil {
-			break
-		}
+		var exportFormat byte
+		exportFormat, err = buf.ReadByte()
 
 		// The indexed export format starts with an 'i'; the older
 		// binary export format starts with a 'c', 'd', or 'v'
 		// (from "version"). Select appropriate importer.
-		if len(data) > 0 && data[0] == 'i' {
-			_, pkg, err = iImportData(fset, packages, data[1:], id)
+		if err == nil && exportFormat == 'i' {
+			pkg, err = iImportData(fset, packages, buf, id)
 		} else {
 			err = fmt.Errorf("import %q: old binary export format no longer supported (recompile library)", path)
 		}
diff --git a/src/go/internal/gcimporter/iimport.go b/src/go/internal/gcimporter/iimport.go
index e003dc9767..b300860e94 100644
--- a/src/go/internal/gcimporter/iimport.go
+++ b/src/go/internal/gcimporter/iimport.go
@@ -8,6 +8,7 @@
 package gcimporter
 
 import (
+	"bufio"
 	"bytes"
 	"encoding/binary"
 	"fmt"
@@ -20,7 +21,7 @@ import (
 )
 
 type intReader struct {
-	*bytes.Reader
+	*bufio.Reader
 	path string
 }
 
@@ -73,7 +74,7 @@ const (
 // and returns the number of bytes consumed and a reference to the package.
 // If the export data version is not recognized or the format is otherwise
 // compromised, an error is returned.
-func iImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (_ int, pkg *types.Package, err error) {
+func iImportData(fset *token.FileSet, imports map[string]*types.Package, dataReader *bufio.Reader, path string) (pkg *types.Package, err error) {
 	const currentVersion = iexportVersionCurrent
 	version := int64(-1)
 	defer func() {
@@ -86,7 +87,7 @@ func iImportData(fset *token.FileSet, imports map[string]*types.Package, data []
 		}
 	}()
 
-	r := &intReader{bytes.NewReader(data), path}
+	r := &intReader{dataReader, path}
 
 	version = int64(r.uint64())
 	switch version {
@@ -102,10 +103,12 @@ func iImportData(fset *token.FileSet, imports map[string]*types.Package, data []
 	sLen := int64(r.uint64())
 	dLen := int64(r.uint64())
 
-	whence, _ := r.Seek(0, io.SeekCurrent)
-	stringData := data[whence : whence+sLen]
-	declData := data[whence+sLen : whence+sLen+dLen]
-	r.Seek(sLen+dLen, io.SeekCurrent)
+	data := make([]byte, sLen+dLen)
+	if _, err := io.ReadFull(r, data); err != nil {
+		errorf("cannot read %d bytes of stringData and declData: %s", len(data), err)
+	}
+	stringData := data[:sLen]
+	declData := data[sLen:]
 
 	p := iimporter{
 		exportVersion: version,
@@ -182,9 +185,7 @@ func iImportData(fset *token.FileSet, imports map[string]*types.Package, data []
 
 	// package was imported completely and without errors
 	localpkg.MarkComplete()
-
-	consumed, _ := r.Seek(0, io.SeekCurrent)
-	return int(consumed), localpkg, nil
+	return localpkg, nil
 }
 
 type iimporter struct {
diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
index 739051cc61..2a2d54da88 100644
--- a/src/go/types/builtins.go
+++ b/src/go/types/builtins.go
@@ -588,6 +588,11 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 
 	case _Add:
 		// unsafe.Add(ptr unsafe.Pointer, len IntegerType) unsafe.Pointer
+		if !check.allowVersion(check.pkg, 1, 17) {
+			check.errorf(call.Fun, _InvalidUnsafeAdd, "unsafe.Add requires go1.17 or later")
+			return
+		}
+
 		check.assignment(x, Typ[UnsafePointer], "argument to unsafe.Add")
 		if x.mode == invalid {
 			return
@@ -684,6 +689,11 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 
 	case _Slice:
 		// unsafe.Slice(ptr *T, len IntegerType) []T
+		if !check.allowVersion(check.pkg, 1, 17) {
+			check.errorf(call.Fun, _InvalidUnsafeSlice, "unsafe.Slice requires go1.17 or later")
+			return
+		}
+
 		typ := asPointer(x.typ)
 		if typ == nil {
 			check.invalidArg(x, _InvalidUnsafeSlice, "%s is not a pointer", x)
diff --git a/src/io/fs/sub.go b/src/io/fs/sub.go
index 7822e555ea..ae20e030a9 100644
--- a/src/io/fs/sub.go
+++ b/src/io/fs/sub.go
@@ -19,10 +19,10 @@ type SubFS interface {
 
 // Sub returns an FS corresponding to the subtree rooted at fsys's dir.
 //
-// If fs implements SubFS, Sub calls returns fsys.Sub(dir).
-// Otherwise, if dir is ".", Sub returns fsys unchanged.
+// If dir is ".", Sub returns fsys unchanged.
+// Otherwise, if fs implements SubFS, Sub returns fsys.Sub(dir).
 // Otherwise, Sub returns a new FS implementation sub that,
-// in effect, implements sub.Open(dir) as fsys.Open(path.Join(dir, name)).
+// in effect, implements sub.Open(name) as fsys.Open(path.Join(dir, name)).
 // The implementation also translates calls to ReadDir, ReadFile, and Glob appropriately.
 //
 // Note that Sub(os.DirFS("/"), "prefix") is equivalent to os.DirFS("/prefix")
diff --git a/src/net/dnsclient_unix_test.go b/src/net/dnsclient_unix_test.go
index a718e75a72..a59be7fea0 100644
--- a/src/net/dnsclient_unix_test.go
+++ b/src/net/dnsclient_unix_test.go
@@ -1898,61 +1898,62 @@ func TestCVE202133195(t *testing.T) {
 	// Change the default resolver to match our manipulated resolver
 	originalDefault := DefaultResolver
 	DefaultResolver = &r
-	defer func() {
-		DefaultResolver = originalDefault
-	}()
+	defer func() { DefaultResolver = originalDefault }()
+	// Redirect host file lookups.
+	defer func(orig string) { testHookHostsPath = orig }(testHookHostsPath)
+	testHookHostsPath = "testdata/hosts"
 
 	_, err := r.LookupCNAME(context.Background(), "golang.org")
 	if expected := "lookup golang.org: CNAME target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("Resolver.LookupCNAME returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("Resolver.LookupCNAME returned unexpected error, got %q, want %q", err, expected)
 	}
 	_, err = LookupCNAME("golang.org")
 	if expected := "lookup golang.org: CNAME target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("LookupCNAME returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("LookupCNAME returned unexpected error, got %q, want %q", err, expected)
 	}
 
 	_, _, err = r.LookupSRV(context.Background(), "target", "tcp", "golang.org")
 	if expected := "lookup golang.org: SRV target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("Resolver.LookupSRV returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("Resolver.LookupSRV returned unexpected error, got %q, want %q", err, expected)
 	}
 	_, _, err = LookupSRV("target", "tcp", "golang.org")
 	if expected := "lookup golang.org: SRV target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("LookupSRV returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("LookupSRV returned unexpected error, got %q, want %q", err, expected)
 	}
 
 	_, _, err = r.LookupSRV(context.Background(), "hdr", "tcp", "golang.org")
 	if expected := "lookup golang.org: SRV header name is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("Resolver.LookupSRV returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("Resolver.LookupSRV returned unexpected error, got %q, want %q", err, expected)
 	}
 	_, _, err = LookupSRV("hdr", "tcp", "golang.org")
 	if expected := "lookup golang.org: SRV header name is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("LookupSRV returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("LookupSRV returned unexpected error, got %q, want %q", err, expected)
 	}
 
 	_, err = r.LookupMX(context.Background(), "golang.org")
 	if expected := "lookup golang.org: MX target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("Resolver.LookupMX returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("Resolver.LookupMX returned unexpected error, got %q, want %q", err, expected)
 	}
 	_, err = LookupMX("golang.org")
 	if expected := "lookup golang.org: MX target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("LookupMX returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("LookupMX returned unexpected error, got %q, want %q", err, expected)
 	}
 
 	_, err = r.LookupNS(context.Background(), "golang.org")
 	if expected := "lookup golang.org: NS target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("Resolver.LookupNS returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("Resolver.LookupNS returned unexpected error, got %q, want %q", err, expected)
 	}
 	_, err = LookupNS("golang.org")
 	if expected := "lookup golang.org: NS target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("LookupNS returned unexpected error, got %q, want %q", err.Error(), expected)
+		t.Errorf("LookupNS returned unexpected error, got %q, want %q", err, expected)
 	}
 
-	_, err = r.LookupAddr(context.Background(), "1.2.3.4")
-	if expected := "lookup 1.2.3.4: PTR target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("Resolver.LookupAddr returned unexpected error, got %q, want %q", err.Error(), expected)
+	_, err = r.LookupAddr(context.Background(), "192.0.2.42")
+	if expected := "lookup 192.0.2.42: PTR target is invalid"; err == nil || err.Error() != expected {
+		t.Errorf("Resolver.LookupAddr returned unexpected error, got %q, want %q", err, expected)
 	}
-	_, err = LookupAddr("1.2.3.4")
-	if expected := "lookup 1.2.3.4: PTR target is invalid"; err == nil || err.Error() != expected {
-		t.Errorf("LookupAddr returned unexpected error, got %q, want %q", err.Error(), expected)
+	_, err = LookupAddr("192.0.2.42")
+	if expected := "lookup 192.0.2.42: PTR target is invalid"; err == nil || err.Error() != expected {
+		t.Errorf("LookupAddr returned unexpected error, got %q, want %q", err, expected)
 	}
 }
diff --git a/src/net/http/server.go b/src/net/http/server.go
index 4e73508973..430019de50 100644
--- a/src/net/http/server.go
+++ b/src/net/http/server.go
@@ -577,37 +577,17 @@ func (w *response) ReadFrom(src io.Reader) (n int64, err error) {
 		return io.CopyBuffer(writerOnly{w}, src, buf)
 	}
 
-	// sendfile path:
-
-	// Do not start actually writing response until src is readable.
-	// If body length is <= sniffLen, sendfile/splice path will do
-	// little anyway. This small read also satisfies sniffing the
-	// body in case Content-Type is missing.
-	nr, er := src.Read(buf[:sniffLen])
-	atEOF := errors.Is(er, io.EOF)
-	n += int64(nr)
-
-	if nr > 0 {
-		// Write the small amount read normally.
-		nw, ew := w.Write(buf[:nr])
-		if ew != nil {
-			err = ew
-		} else if nr != nw {
-			err = io.ErrShortWrite
+	// Copy the first sniffLen bytes before switching to ReadFrom.
+	// This ensures we don't start writing the response before the
+	// source is available (see golang.org/issue/5660) and provides
+	// enough bytes to perform Content-Type sniffing when required.
+	if !w.cw.wroteHeader {
+		n0, err := io.CopyBuffer(writerOnly{w}, io.LimitReader(src, sniffLen), buf)
+		n += n0
+		if err != nil || n0 < sniffLen {
+			return n, err
 		}
 	}
-	if err == nil && er != nil && !atEOF {
-		err = er
-	}
-
-	// Do not send StatusOK in the error case where nothing has been written.
-	if err == nil && !w.wroteHeader {
-		w.WriteHeader(StatusOK) // nr == 0, no error (or EOF)
-	}
-
-	if err != nil || atEOF {
-		return n, err
-	}
 
 	w.w.Flush()  // get rid of any previous writes
 	w.cw.flush() // make sure Header is written; flush data to rwc
@@ -620,7 +600,7 @@ func (w *response) ReadFrom(src io.Reader) (n int64, err error) {
 		return n, err
 	}
 
-	n0, err := io.Copy(writerOnly{w}, src)
+	n0, err := io.CopyBuffer(writerOnly{w}, src, buf)
 	n += n0
 	return n, err
 }
diff --git a/src/net/http/sniff_test.go b/src/net/http/sniff_test.go
index 8d5350374d..e91335729a 100644
--- a/src/net/http/sniff_test.go
+++ b/src/net/http/sniff_test.go
@@ -157,9 +157,25 @@ func testServerIssue5953(t *testing.T, h2 bool) {
 	resp.Body.Close()
 }
 
-func TestContentTypeWithCopy_h1(t *testing.T) { testContentTypeWithCopy(t, h1Mode) }
-func TestContentTypeWithCopy_h2(t *testing.T) { testContentTypeWithCopy(t, h2Mode) }
-func testContentTypeWithCopy(t *testing.T, h2 bool) {
+type byteAtATimeReader struct {
+	buf []byte
+}
+
+func (b *byteAtATimeReader) Read(p []byte) (n int, err error) {
+	if len(p) < 1 {
+		return 0, nil
+	}
+	if len(b.buf) == 0 {
+		return 0, io.EOF
+	}
+	p[0] = b.buf[0]
+	b.buf = b.buf[1:]
+	return 1, nil
+}
+
+func TestContentTypeWithVariousSources_h1(t *testing.T) { testContentTypeWithVariousSources(t, h1Mode) }
+func TestContentTypeWithVariousSources_h2(t *testing.T) { testContentTypeWithVariousSources(t, h2Mode) }
+func testContentTypeWithVariousSources(t *testing.T, h2 bool) {
 	defer afterTest(t)
 
 	const (
@@ -167,30 +183,86 @@ func testContentTypeWithCopy(t *testing.T, h2 bool) {
 		expected = "text/html; charset=utf-8"
 	)
 
-	cst := newClientServerTest(t, h2, HandlerFunc(func(w ResponseWriter, r *Request) {
-		// Use io.Copy from a bytes.Buffer to trigger ReadFrom.
-		buf := bytes.NewBuffer([]byte(input))
-		n, err := io.Copy(w, buf)
-		if int(n) != len(input) || err != nil {
-			t.Errorf("io.Copy(w, %q) = %v, %v want %d, nil", input, n, err, len(input))
-		}
-	}))
-	defer cst.close()
+	for _, test := range []struct {
+		name    string
+		handler func(ResponseWriter, *Request)
+	}{{
+		name: "write",
+		handler: func(w ResponseWriter, r *Request) {
+			// Write the whole input at once.
+			n, err := w.Write([]byte(input))
+			if int(n) != len(input) || err != nil {
+				t.Errorf("w.Write(%q) = %v, %v want %d, nil", input, n, err, len(input))
+			}
+		},
+	}, {
+		name: "write one byte at a time",
+		handler: func(w ResponseWriter, r *Request) {
+			// Write the input one byte at a time.
+			buf := []byte(input)
+			for i := range buf {
+				n, err := w.Write(buf[i : i+1])
+				if n != 1 || err != nil {
+					t.Errorf("w.Write(%q) = %v, %v want 1, nil", input, n, err)
+				}
+			}
+		},
+	}, {
+		name: "copy from Reader",
+		handler: func(w ResponseWriter, r *Request) {
+			// Use io.Copy from a plain Reader.
+			type readerOnly struct{ io.Reader }
+			buf := bytes.NewBuffer([]byte(input))
+			n, err := io.Copy(w, readerOnly{buf})
+			if int(n) != len(input) || err != nil {
+				t.Errorf("io.Copy(w, %q) = %v, %v want %d, nil", input, n, err, len(input))
+			}
+		},
+	}, {
+		name: "copy from bytes.Buffer",
+		handler: func(w ResponseWriter, r *Request) {
+			// Use io.Copy from a bytes.Buffer to trigger ReadFrom.
+			buf := bytes.NewBuffer([]byte(input))
+			n, err := io.Copy(w, buf)
+			if int(n) != len(input) || err != nil {
+				t.Errorf("io.Copy(w, %q) = %v, %v want %d, nil", input, n, err, len(input))
+			}
+		},
+	}, {
+		name: "copy one byte at a time",
+		handler: func(w ResponseWriter, r *Request) {
+			// Use io.Copy from a Reader that returns one byte at a time.
+			n, err := io.Copy(w, &byteAtATimeReader{[]byte(input)})
+			if int(n) != len(input) || err != nil {
+				t.Errorf("io.Copy(w, %q) = %v, %v want %d, nil", input, n, err, len(input))
+			}
+		},
+	}} {
+		t.Run(test.name, func(t *testing.T) {
+			cst := newClientServerTest(t, h2, HandlerFunc(test.handler))
+			defer cst.close()
+
+			resp, err := cst.c.Get(cst.ts.URL)
+			if err != nil {
+				t.Fatalf("Get: %v", err)
+			}
+			if ct := resp.Header.Get("Content-Type"); ct != expected {
+				t.Errorf("Content-Type = %q, want %q", ct, expected)
+			}
+			if want, got := resp.Header.Get("Content-Length"), fmt.Sprint(len(input)); want != got {
+				t.Errorf("Content-Length = %q, want %q", want, got)
+			}
+			data, err := io.ReadAll(resp.Body)
+			if err != nil {
+				t.Errorf("reading body: %v", err)
+			} else if !bytes.Equal(data, []byte(input)) {
+				t.Errorf("data is %q, want %q", data, input)
+			}
+			resp.Body.Close()
+
+		})
 
-	resp, err := cst.c.Get(cst.ts.URL)
-	if err != nil {
-		t.Fatalf("Get: %v", err)
-	}
-	if ct := resp.Header.Get("Content-Type"); ct != expected {
-		t.Errorf("Content-Type = %q, want %q", ct, expected)
-	}
-	data, err := io.ReadAll(resp.Body)
-	if err != nil {
-		t.Errorf("reading body: %v", err)
-	} else if !bytes.Equal(data, []byte(input)) {
-		t.Errorf("data is %q, want %q", data, input)
 	}
-	resp.Body.Close()
 }
 
 func TestSniffWriteSize_h1(t *testing.T) { testSniffWriteSize(t, h1Mode) }
diff --git a/src/os/exec_windows.go b/src/os/exec_windows.go
index 5710401acd..239bed198f 100644
--- a/src/os/exec_windows.go
+++ b/src/os/exec_windows.go
@@ -45,16 +45,6 @@ func (p *Process) wait() (ps *ProcessState, err error) {
 	return &ProcessState{p.Pid, syscall.WaitStatus{ExitCode: ec}, &u}, nil
 }
 
-func terminateProcess(pid, exitcode int) error {
-	h, e := syscall.OpenProcess(syscall.PROCESS_TERMINATE, false, uint32(pid))
-	if e != nil {
-		return NewSyscallError("OpenProcess", e)
-	}
-	defer syscall.CloseHandle(h)
-	e = syscall.TerminateProcess(h, uint32(exitcode))
-	return NewSyscallError("TerminateProcess", e)
-}
-
 func (p *Process) signal(sig Signal) error {
 	handle := atomic.LoadUintptr(&p.handle)
 	if handle == uintptr(syscall.InvalidHandle) {
@@ -64,16 +54,22 @@ func (p *Process) signal(sig Signal) error {
 		return ErrProcessDone
 	}
 	if sig == Kill {
-		err := terminateProcess(p.Pid, 1)
+		var terminationHandle syscall.Handle
+		e := syscall.DuplicateHandle(^syscall.Handle(0), syscall.Handle(handle), ^syscall.Handle(0), &terminationHandle, syscall.PROCESS_TERMINATE, false, 0)
+		if e != nil {
+			return NewSyscallError("DuplicateHandle", e)
+		}
 		runtime.KeepAlive(p)
-		return err
+		defer syscall.CloseHandle(terminationHandle)
+		e = syscall.TerminateProcess(syscall.Handle(terminationHandle), 1)
+		return NewSyscallError("TerminateProcess", e)
 	}
 	// TODO(rsc): Handle Interrupt too?
 	return syscall.Errno(syscall.EWINDOWS)
 }
 
 func (p *Process) release() error {
-	handle := atomic.LoadUintptr(&p.handle)
+	handle := atomic.SwapUintptr(&p.handle, uintptr(syscall.InvalidHandle))
 	if handle == uintptr(syscall.InvalidHandle) {
 		return syscall.EINVAL
 	}
@@ -81,7 +77,6 @@ func (p *Process) release() error {
 	if e != nil {
 		return NewSyscallError("CloseHandle", e)
 	}
-	atomic.StoreUintptr(&p.handle, uintptr(syscall.InvalidHandle))
 	// no need for a finalizer anymore
 	runtime.SetFinalizer(p, nil)
 	return nil
diff --git a/src/runtime/internal/sys/gengoos.go b/src/runtime/internal/sys/gengoos.go
index 51f64a6e5c..ffe962f71d 100644
--- a/src/runtime/internal/sys/gengoos.go
+++ b/src/runtime/internal/sys/gengoos.go
@@ -48,18 +48,21 @@ func main() {
 		if target == "nacl" {
 			continue
 		}
-		var buf bytes.Buffer
-		fmt.Fprintf(&buf, "// Code generated by gengoos.go using 'go generate'. DO NOT EDIT.\n\n")
+		var tags []string
 		if target == "linux" {
-			fmt.Fprintf(&buf, "// +build !android\n") // must explicitly exclude android for linux
+			tags = append(tags, "!android") // must explicitly exclude android for linux
 		}
 		if target == "solaris" {
-			fmt.Fprintf(&buf, "// +build !illumos\n") // must explicitly exclude illumos for solaris
+			tags = append(tags, "!illumos") // must explicitly exclude illumos for solaris
 		}
 		if target == "darwin" {
-			fmt.Fprintf(&buf, "// +build !ios\n") // must explicitly exclude ios for darwin
+			tags = append(tags, "!ios") // must explicitly exclude ios for darwin
 		}
-		fmt.Fprintf(&buf, "// +build %s\n\n", target) // must explicitly include target for bootstrapping purposes
+		tags = append(tags, target) // must explicitly include target for bootstrapping purposes
+		var buf bytes.Buffer
+		fmt.Fprintf(&buf, "// Code generated by gengoos.go using 'go generate'. DO NOT EDIT.\n\n")
+		fmt.Fprintf(&buf, "//go:build %s\n", strings.Join(tags, " && "))
+		fmt.Fprintf(&buf, "// +build %s\n\n", strings.Join(tags, ","))
 		fmt.Fprintf(&buf, "package sys\n\n")
 		fmt.Fprintf(&buf, "const GOOS = `%s`\n\n", target)
 		for _, goos := range gooses {
@@ -81,6 +84,7 @@ func main() {
 		}
 		var buf bytes.Buffer
 		fmt.Fprintf(&buf, "// Code generated by gengoos.go using 'go generate'. DO NOT EDIT.\n\n")
+		fmt.Fprintf(&buf, "//go:build %s\n", target)
 		fmt.Fprintf(&buf, "// +build %s\n\n", target) // must explicitly include target for bootstrapping purposes
 		fmt.Fprintf(&buf, "package sys\n\n")
 		fmt.Fprintf(&buf, "const GOARCH = `%s`\n\n", target)
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 63eeb6c9c7..24566e5efa 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -4071,8 +4071,16 @@ func exitsyscall0(gp *g) {
 	if schedEnabled(gp) {
 		_p_ = pidleget()
 	}
+	var locked bool
 	if _p_ == nil {
 		globrunqput(gp)
+
+		// Below, we stoplockedm if gp is locked. globrunqput releases
+		// ownership of gp, so we must check if gp is locked prior to
+		// committing the release by unlocking sched.lock, otherwise we
+		// could race with another M transitioning gp from unlocked to
+		// locked.
+		locked = gp.lockedm != 0
 	} else if atomic.Load(&sched.sysmonwait) != 0 {
 		atomic.Store(&sched.sysmonwait, 0)
 		notewakeup(&sched.sysmonnote)
@@ -4082,7 +4090,7 @@ func exitsyscall0(gp *g) {
 		acquirep(_p_)
 		execute(gp, false) // Never returns.
 	}
-	if gp.lockedm != 0 {
+	if locked {
 		// Wait until another thread schedules gp and so m again.
 		//
 		// N.B. lockedm must be this M, as this g was running on this M
diff --git a/src/syscall/exec_windows.go b/src/syscall/exec_windows.go
index 253e9e8c1f..18d15028c3 100644
--- a/src/syscall/exec_windows.go
+++ b/src/syscall/exec_windows.go
@@ -313,6 +313,17 @@ func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle
 		}
 	}
 
+	var maj, min, build uint32
+	rtlGetNtVersionNumbers(&maj, &min, &build)
+	isWin7 := maj < 6 || (maj == 6 && min <= 1)
+	// NT kernel handles are divisible by 4, with the bottom 3 bits left as
+	// a tag. The fully set tag correlates with the types of handles we're
+	// concerned about here.  Except, the kernel will interpret some
+	// special handle values, like -1, -2, and so forth, so kernelbase.dll
+	// checks to see that those bottom three bits are checked, but that top
+	// bit is not checked.
+	isLegacyWin7ConsoleHandle := func(handle Handle) bool { return isWin7 && handle&0x10000003 == 3 }
+
 	p, _ := GetCurrentProcess()
 	parentProcess := p
 	if sys.ParentProcess != 0 {
@@ -321,7 +332,15 @@ func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle
 	fd := make([]Handle, len(attr.Files))
 	for i := range attr.Files {
 		if attr.Files[i] > 0 {
-			err := DuplicateHandle(p, Handle(attr.Files[i]), parentProcess, &fd[i], 0, true, DUPLICATE_SAME_ACCESS)
+			destinationProcessHandle := parentProcess
+
+			// On Windows 7, console handles aren't real handles, and can only be duplicated
+			// into the current process, not a parent one, which amounts to the same thing.
+			if parentProcess != p && isLegacyWin7ConsoleHandle(Handle(attr.Files[i])) {
+				destinationProcessHandle = p
+			}
+
+			err := DuplicateHandle(p, Handle(attr.Files[i]), destinationProcessHandle, &fd[i], 0, true, DUPLICATE_SAME_ACCESS)
 			if err != nil {
 				return 0, 0, err
 			}
@@ -351,19 +370,40 @@ func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle
 	si.StdErr = fd[2]
 
 	fd = append(fd, sys.AdditionalInheritedHandles...)
+
+	// On Windows 7, console handles aren't real handles, so don't pass them
+	// through to PROC_THREAD_ATTRIBUTE_HANDLE_LIST.
+	for i := range fd {
+		if isLegacyWin7ConsoleHandle(fd[i]) {
+			fd[i] = 0
+		}
+	}
+
+	// The presence of a NULL handle in the list is enough to cause PROC_THREAD_ATTRIBUTE_HANDLE_LIST
+	// to treat the entire list as empty, so remove NULL handles.
+	j := 0
+	for i := range fd {
+		if fd[i] != 0 {
+			fd[j] = fd[i]
+			j++
+		}
+	}
+	fd = fd[:j]
+
 	// Do not accidentally inherit more than these handles.
-	err = updateProcThreadAttribute(si.ProcThreadAttributeList, 0, _PROC_THREAD_ATTRIBUTE_HANDLE_LIST, unsafe.Pointer(&fd[0]), uintptr(len(fd))*unsafe.Sizeof(fd[0]), nil, nil)
-	if err != nil {
-		return 0, 0, err
+	if len(fd) > 0 {
+		err = updateProcThreadAttribute(si.ProcThreadAttributeList, 0, _PROC_THREAD_ATTRIBUTE_HANDLE_LIST, unsafe.Pointer(&fd[0]), uintptr(len(fd))*unsafe.Sizeof(fd[0]), nil, nil)
+		if err != nil {
+			return 0, 0, err
+		}
 	}
 
 	pi := new(ProcessInformation)
-
 	flags := sys.CreationFlags | CREATE_UNICODE_ENVIRONMENT | _EXTENDED_STARTUPINFO_PRESENT
 	if sys.Token != 0 {
-		err = CreateProcessAsUser(sys.Token, argv0p, argvp, sys.ProcessAttributes, sys.ThreadAttributes, !sys.NoInheritHandles, flags, createEnvBlock(attr.Env), dirp, &si.StartupInfo, pi)
+		err = CreateProcessAsUser(sys.Token, argv0p, argvp, sys.ProcessAttributes, sys.ThreadAttributes, len(fd) > 0 && !sys.NoInheritHandles, flags, createEnvBlock(attr.Env), dirp, &si.StartupInfo, pi)
 	} else {
-		err = CreateProcess(argv0p, argvp, sys.ProcessAttributes, sys.ThreadAttributes, !sys.NoInheritHandles, flags, createEnvBlock(attr.Env), dirp, &si.StartupInfo, pi)
+		err = CreateProcess(argv0p, argvp, sys.ProcessAttributes, sys.ThreadAttributes, len(fd) > 0 && !sys.NoInheritHandles, flags, createEnvBlock(attr.Env), dirp, &si.StartupInfo, pi)
 	}
 	if err != nil {
 		return 0, 0, err
diff --git a/src/syscall/syscall_windows.go b/src/syscall/syscall_windows.go
index fc734effbb..660179ae9e 100644
--- a/src/syscall/syscall_windows.go
+++ b/src/syscall/syscall_windows.go
@@ -198,6 +198,7 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	FreeLibrary(handle Handle) (err error)
 //sys	GetProcAddress(module Handle, procname string) (proc uintptr, err error)
 //sys	GetVersion() (ver uint32, err error)
+//sys	rtlGetNtVersionNumbers(majorVersion *uint32, minorVersion *uint32, buildNumber *uint32) = ntdll.RtlGetNtVersionNumbers
 //sys	formatMessage(flags uint32, msgsrc uintptr, msgid uint32, langid uint32, buf []uint16, args *byte) (n uint32, err error) = FormatMessageW
 //sys	ExitProcess(exitcode uint32)
 //sys	CreateFile(name *uint16, access uint32, mode uint32, sa *SecurityAttributes, createmode uint32, attrs uint32, templatefile int32) (handle Handle, err error) [failretval==InvalidHandle] = CreateFileW
diff --git a/src/syscall/zsyscall_windows.go b/src/syscall/zsyscall_windows.go
index 10d0f54e8c..7bfff16be6 100644
--- a/src/syscall/zsyscall_windows.go
+++ b/src/syscall/zsyscall_windows.go
@@ -43,6 +43,7 @@ var (
 	modkernel32 = NewLazyDLL(sysdll.Add("kernel32.dll"))
 	modmswsock  = NewLazyDLL(sysdll.Add("mswsock.dll"))
 	modnetapi32 = NewLazyDLL(sysdll.Add("netapi32.dll"))
+	modntdll    = NewLazyDLL(sysdll.Add("ntdll.dll"))
 	modsecur32  = NewLazyDLL(sysdll.Add("secur32.dll"))
 	modshell32  = NewLazyDLL(sysdll.Add("shell32.dll"))
 	moduserenv  = NewLazyDLL(sysdll.Add("userenv.dll"))
@@ -167,6 +168,7 @@ var (
 	procNetApiBufferFree                   = modnetapi32.NewProc("NetApiBufferFree")
 	procNetGetJoinInformation              = modnetapi32.NewProc("NetGetJoinInformation")
 	procNetUserGetInfo                     = modnetapi32.NewProc("NetUserGetInfo")
+	procRtlGetNtVersionNumbers             = modntdll.NewProc("RtlGetNtVersionNumbers")
 	procGetUserNameExW                     = modsecur32.NewProc("GetUserNameExW")
 	procTranslateNameW                     = modsecur32.NewProc("TranslateNameW")
 	procCommandLineToArgvW                 = modshell32.NewProc("CommandLineToArgvW")
@@ -1213,6 +1215,11 @@ func NetUserGetInfo(serverName *uint16, userName *uint16, level uint32, buf **by
 	return
 }
 
+func rtlGetNtVersionNumbers(majorVersion *uint32, minorVersion *uint32, buildNumber *uint32) {
+	Syscall(procRtlGetNtVersionNumbers.Addr(), 3, uintptr(unsafe.Pointer(majorVersion)), uintptr(unsafe.Pointer(minorVersion)), uintptr(unsafe.Pointer(buildNumber)))
+	return
+}
+
 func GetUserNameEx(nameFormat uint32, nameBuffre *uint16, nSize *uint32) (err error) {
 	r1, _, e1 := Syscall(procGetUserNameExW.Addr(), 3, uintptr(nameFormat), uintptr(unsafe.Pointer(nameBuffre)), uintptr(unsafe.Pointer(nSize)))
 	if r1&0xff == 0 {
diff --git a/test/fixedbugs/issue46525.go b/test/fixedbugs/issue46525.go
new file mode 100644
index 0000000000..164e1473ce
--- /dev/null
+++ b/test/fixedbugs/issue46525.go
@@ -0,0 +1,14 @@
+// errorcheck -lang=go1.16
+
+// Copyright 2021 The Go Authors. All rights reserved.  Use of this
+// source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package p
+
+import "unsafe"
+
+func main() {
+	_ = unsafe.Add(unsafe.Pointer(nil), 0) // ERROR "unsafe.Add requires go1.17 or later"
+	_ = unsafe.Slice(new(byte), 1)         // ERROR "unsafe.Slice requires go1.17 or later"
+}